Antenna system



W. E- BRADLEY ANTENNA SYSTEM Jan. 3L 195@ Filed July 22, 1944 INVENTOR.VVzZ/fam Efi aa/sg Patented Jan. 31, 1950' UNITED STATES ANTENNA SYSTEMWilliam E. Bradley, Swarthmore, Pa., assignor, by mesne assignments, toPhilco Corporation, Philadelphia, Pa., a corporation of Pennsylvania.

Application July 22, 1944, Serial N 0. 546,181

24 Glaims. 1

My invention relates in general to the field of signalling systems andmore particularly concerns a novel and improved antenna structure.

In high frequency transmission systems, en ergy is ordinarily radiatedfrom an antenna array suitably supported and fed from a resonanttransmission line. The nature of the antenna structure is of coursedependent upon the desired type of transmission.

The feeding system generally comprises a coaxial transmission lineproperly terminated and tuned by matching stubs so that a maximum energytransfer may occur. In certain ultra-high frequency transmissionsystems, as for example, radio ranging or radar, it is particularlydesirable to utilize a duplex transmission system re quiring two antennaarrays. Heretofore, in the energization of such a double antennastructure, numerous problems have arisen which were primarily concernedwith the mutual interference of the electrical feeders and the antennaradiating structure. Thus, for example, if two antenna ar rays werestacked one above the other, and en ergized from individual coaxialfeeders, then the feeder for the upper array would interfere withradiation from the lower antenna array.

Accordingly it has generally been essential that the antenna arrays beseparated or that the feeders be energized from opposite ends of theduplex antenna structure. This of course unnecessarily complicated thesupport of antenna structures upon towers, masts and the like.

My invention contemplates'and has as a primary object an antenna feedingsystem which permits the stacking of a plurality of antenna arrays, allof which are energized from a single end thereof, and which precludemutual interference between antenna radiation and feeder systems. Eachindividual antenna array consists of a coaxial resonator short circuitedat theupper end and driven from the lower end by a coaxial line withdipole elements coupled into the resonator at half wave intervals alongthe resonator.

Individual coaxial feed lines are provided for each of the antennaarrays, and may be driven from suitable oscillating sources. The innercon ductor of the resonator for the lower antenna array is hollow andsupports therein an additional concentric feeder which extends upthrough the lower antenna structure and enters the coaxial resonator ofthe upper antenna array. This last mentioned inner feeder is energizedfrom the oscillating system feeding the upper antenna structure andaccordingly serves as the transmission line for the upper antenna structure.

The lower antenna structure is properly matched by a tuning stubconnected to the coaxia1 resonator associated with the lower antennastructure. This tuning stub which also may be fed in the manner to bedescribed,

contains the central conductor of the lower antenna structure serves asa suitable means for removing the central feeder for the upper antennastructure from the stacked array of antennae. Accordingly, both antennaarrays are fed from a single end of the multiple structure.

The proper terminating characteristic impedance for each of the twoantenna structures is maintained by suitably dimensioning the feedingsystem, and by properly coupling each antenna element to the coaxialresonators associated therewith.

It is thus an object of my invention to provide a novel and improvedduplex antenna structure.

Another object of my invention is to provide a duplex antenna structureenergized from a single end thereof without mutual interference.

A further object of my invention is to provide a. multiple antennaradiating structure wherein a plurality of concentrically disposedconductors are utilized to feed the individual antenna radiatingstructures without mutual interference.

These and other objects of my invention will now become apparent fromthe following detailed specification taken in connection with. theaccompanying drawings in which:

Figure 1 is a cross-sectional schematic view of one modification of aduplex antenna.

Figure 2 is a cross-sectional schematic view of a modification of theduplex antenna principle i1- lustrated in Figure 1.

Referring now to Figure 1, the mechanical detail of a duplex antennastructure will now be described. As illustrated, a metallic structure Ii is utilized as the principal support for the double antenna array.This metal member may of course be mounted suitably upon a tower or uponthe mast of a ship or the like, dependent upon the particularapplication of the duplex transmission system. Supported upon themetallic structure I l are the two antenna arrays No. l and No. 2 to beutilized during the transmission or reception of signals, and comprisingessentially, a lower array of antenna elements l2 and an upper array ofantenna elements l3. These individual antenna elements illustrated at 12and 53 are rigidly supported upon the metallic structure l l, andsuitably insulated therefrom. The driving terminals of the unit antennaelements shown at it and 13 enter the outer metallic structure I 5through suitable apertures, such as l4.

It is to be understood that the antenna arrays I2 and is illustrated inFigure 1 are merely rep-' resentations of possible antenna structures.As there are many types of antenna arrays which the number anddisposition of the antenna elements 1!? and #3 are, of course, dependentupon the directional character of the radiation and the locationthereof. Other than indicating a possible modification of my duplexantenna structure, these schematic illustrations of antenna elements ati2 and I3 played no part in the fundamental considerations of thepresent invention.

A suitable coupling I5 is provided at the lower end of the metallicstructure it for a feeder which is connected to the transmission circuitof the apparatus concerned. This feeder may comprise a coaxial cablecoupled tothe duplex antenna structure by a connection at coupling l5 sothat the outer sheet of the coaxial cable contacts the metallic outerstructure H and the inner concentric conductor of th coaxial cablecontacts concentric conductor ll rigidly supported within the metallicstructure H. Thus, throughout the lower antenna array No. 1, the innerand outer concentric metallic members ll and I! respectively form acoaxial resonator 2! into which the antenna elements i2 are coupled.

At the upper end of the lower antenna array No. l a metal insert 22 isprovided to seal the cylindrical resonator between the concentricmembers H and H.

in order to insure the transfer of maximum energy from the coaxialfeeder coupled to the duplex antenna structure at 5 to the lower antennaarray 12, it is essential that the chamber 2! be properly matched ortuned. Accordingly, a matching section 25 is connected to metallicmember I l at the aperture 23 therein. Similarly, a hollow conductor 21concentric with and extending from section 25 is connected to the innerconcentric conductor [1 at an aperture 26 thereof.

The coaxial conductors 25 and 21 form an annular chamber 31 within whichis mounted an annular member 32 axially movable therein.

From the above structural description, it will now be evident that theinput impedance to the antenna array No. l is controlled by the amountof penetration of the driving terminals of the antenna elements l2through the apertures [4 as well as by the specific design of theantenna elements. movement of the annulus 32 which in practice has amean position approximately wave length from aperture 23. p

The exact length of the stub chamber 3| will transmission system. Forthe upper antenna array No. 2. the innermostcoriductor 44 and itsconductive shield ll provide the necessary feeder circuit.

Ihe central conductor 44 as stated is concentrically located withinconductive shield 11 and is maintained in this position by a pluralityof solid dielectric spacers as, for example, 5!, which may be madeone-half wave length long to preclude undesirable impedance mismatchesalong the line.

At point 52 of the innermost conductor 44, an extension lead 53 isjoined thereto. 52 is located on the longitudinal axis of the matchingstub and accordingly within the matching stub 25 an arrangement of threeconcentric conductors eXistsas in the main section of the antennastructure/ The conductor 53 extends through its shielding conductor 27and beyond the matching stub 25 and terminates at the coupling unit 54which comprises essentially a threaded section of the conductor 21. v

The outer shield 250i the matching stub is extended at 55 to enclose anadditional section of the shield 21. Accordingly, at coupling unit 54, aconnector from a coaxial cable may be attached so that the shield of thecoaxial cable contacts the innermost conductor 21 of the concentricantenna 7 arrangement.

Thus, energy may be fed from the coaxial cable coupling to the antennastructure at 54 through the coaxial line comprising the centralconductor 53 and the outer conductor 21 to the junction A furthercontrol is provided by axial of course be determined by experimentalmeans.

It is thus clear from the foregoing that the lower antenna arraycomprising the antenna elements I2 is energized by a coaxial feedingsystem cornprising an outer conductor II and an inner concentricconductor IT. This coaxial section of conductors which feeds the unitantenna elements is terminated at 22. The feeding system illustrated forthe unit antenna l2 thus corresponds in many respects to conventionalfeeding systems for a single antenna structure.

The upper end of the outer conductor II, as previously described,supports the antenna elements of the upper antenna array No. 2 and iscapped by a metallic plate 4|. 7

Between the metallic termination 22 and the cap 4! in the outerconductor H, a coaxial resonator 43 is formed by the conductor I l andconductor 42 concentric with conductor II.

The concentric line conductor 42 is the flared extension of feeder 44which extends upwardly along the axis of the cylindrical conductor ll.Accordingly, the concentric feeder system extending through the lowerantenna array comprises three concentrically spaced conductive members.For the lower antenna array No. l, the conductors II and I7 form thenecessary thereof with the central conductor 44 and the outer conductor11. This coaxial system feeds energy up through the antenna structureillustrated to the concentric arrangement of coaxial conductors I l and42 in the upper antenna array As illustrated, the conductor I! is flaredat 6! to connect with conductor H, and the central conductor 44 isflared at 62 to form concentric conductor 42. Hollow concentricconductors H and 42 form therebetween a resonant chamber 43. Thischamber 43 terminates at the upper end thereof in the metallic-cap 41.Although the diameters of the inner and outer conductors of the coaxialsystem feeding the resonant chamber 43 are altered beyond the metallicterminal 22, it is well known that the characteristic impedance of thline may be maintained at a constant value if a proper ratio ofconductive diameters is maintained.

The antenna elements I3 of the upper antenna array No. 2 terminatewithin the chamber 43 between the inner and outer concentric conductorsII and 42 through apertures formed in conductor H and suitably insulatedtherefrom.

The amount of penetration of the driving terminals of the antennaelements 13 through the apertures and the specific design of the antennaelements control the input impedance to antenna array No. 2. A furthercontrol is provided by a tuning stub as will now be described.

At the lower end of the antenna structure, the central conductor i1 isextended below the junction point 52 in order to provide a matching stub63 for the feeder system comprising central conductor 44 and itsassociated shield conductor IT. The matching stub 63 is tuned by ametallic shorting bar 65 which may be experimentally axiallypositionedto provide a matching impedance for the transmission line suchthat maximum energy transfer will take place from the The point input atcoupling unit 54 to the resonant chamber 43 of the upper antenna arrayNo. 2. The member 65 (Figure 1)- will in practice have a mean positionapproximately wave length from aperture 26.

It is thus evident that at coupling unit 54 a concentric line may bejointed thereto in order to energize the upper antenna array No. 2. Theenergy transmitted to the upper antenna array is confined entirely to anelectromagnetic field within conductor H. In this manner, theelectromagnetic energy fed to resonator section 43 extends concentricwith the resonator energizing the lower antenna array No. l, but, as isevident from Figure I, cannot affect the field within resonator 2!. Thefield within resonator 2! is in turn energized by a coaxial systemextending from coupling unit I5 and comprising the outer metallic shieldl l and the concentric conductor 11.

Thus, the conductor ll acts as a common dividing barrier and restrictsthe electromagnetic en ergy to the space between itself and either ofthe concentric conductors shown.

Since each of the feeding systems for the antenna arrays is completelyshielded from the other feeding systems, mutual interference iscompletely eliminated. Furthermore, within each of the coupling unitsfor the antenna arrays, a matching stub is provided for the resonator ofthe other antenna array.

It is evident that the antenna arrays No. 1 and No. 2 may be energizedsingly or simultaneously at different frequencies without cross-couplingtherebetween. They may simultaneously transmit or receive or maysimultaneously transmit over one antenna array and receive on the otherantenna array.

The basic concept illustrated in Figure l of a multiple of concentricfeeders for an antenna array may be applied to antenna structures invarious different manners.

As illustrated in Figure 2, the three concentric conductors may beutilized to energize a single antenna array in such a manner that energyis fed into the center of the unit antenna structure. The application ofenergy to a radiating system in this manner is of particular advantagewhere broad band transmission characteristics for an antenna system aredesired. As illustrated, an outer hollow conductor H encloses twoconcentric conductors l2 and 13 which extend to. the center 74 of anarray of antenna elements 15 suitably insulated and supported inapertures 10. Of course, as previously mentioned, the antenna arrayutilized and the extent of penetration thereof through apertures l0 willdepend upon the type of transmission characteristics desired, and is notto be considered as part of the present invention.

At point 16 of the innermost conductor '13, an enlarged diameter hollowconductor 11 is attached and extends to the top of the radiatingstructure. The attached conductor 1! of increased diameter correspondsessentially to the central hollow conductor 12 which terminates at 1B.The energy to be radiated is fed into this antenna structure through thesmall diameter transmission line formed by the central conductor 13 andits enclosing shield 12.

A suitable coupling unit for a coaxial line which in turn is coupled tothe oscillating system may be provided. Energy is transmitted up thiscoaxial system to point 18 at which point it enters the resonant chamberBl between enlarged diameter section 11 andthe outer shield H, andresonant chamber 82. between the shield ll and the concentric conductor12. It is evident therefore that energy flows from the termination. 18of the small diameter coaxial field transmission line to the upperandIlower section of resonant chamber 8i, and accordingly is fed to thecenter pletely avoided. The duplex antenna structure illustrated anddescribed above is of course subject to many modifications withoutaltering the basic. concept of absence of cross-coupling and otherinterference. a i

I thus prefer not to be bound by the specific disclosures hereinaboveset forth, but only by the appended claims.

I claim: i i

1. In a system for feeding a plurality of antenna arrays; a first pairof concentric conductors, an antenna array terminating. in the chamberformed by said concentricconductors; a second pair of concentricconductors, an extension of the inner conductor of said first pairconstituting the outer conductor of said second pair of concentricconductors and an antenna array terminating in the chamber formed bysaid second pair of concentric conductors.

2. In a system for feeding a plurality of antenna arrays; a firstresonant hollow chamber comprising a first outer cylindrical wall, afirs inner concentric wall forming with said outer cylindrical wallsaid, first resonant hollow chamber and having a closed end and having acircuit connection at its opposite end for electrically exciting saidfirst chamber, a second resonant hollow chamber comprising a secondouter cylindrical wall, a second inner concentric wall forming with,said second outer cylindrical wall said second resonant hollow chamber,said second chamber being mounted in axial alignment with said firstchamber and having a circuit connection at its end juxtaposed to saidfirst chamber for electri-- cally exciting said second chamber. a 3'. Ina. system for feeding a; plurality of antenna arrays; a first resonantchamber comprising a cylindrical wall member and having a closed end andhaving a, circuit connection at its opposite end for electricallyexciting said chamber, a second resonant chamber comprising acylindrical wall member mounted in axial alignment with said firstchamber and having a circuit connection at its end juxtaposed to saidfirst chamber for electrically exciting said second chamber, and meanswhereby said last mentioned circuit connection extends longitudinallyalong said first chamber without electrical interference therewith.

4. In a system for feedinga plurality of ans tenna arrays; a pluralityof hollow resonant chambers in axial alignment; each chamber comprisingcylindrical wall members; circuit means for independently excitingeachof said antenna arrays from one end. of said axially alignedchambers, and means rorpreventing terference between said exciting meansor one of said resonant chambers and any other resonant chamber.

5. In a system for feeding a plurality of antenna arrays; a plurality ofhollow resonant chambers, each of said chambers being formed between aninner and outer concentric wall, the extension of the inner concentricwall comprising a wall of another of said chambers and conductor meansextending along the axis of said one of said chambers for feedingcurrent to said another of said chambers.

6. In a system for feeding a plurality of antenna arrays; a plurality ofhollow resonant chambers in axial alignment; each chamber comprisingcylindrical wall members; circuit means for independently exciting eachof said antenna arrays from one end of said axially aligned chambers anda shield extending along the longitudinal axis of said chambers for saidcircuit means.

7. In a system, a plurality of antenna arrays; a plurality of hollowresonant chambers in axial alignment; each chamber comprisingcylindrical wall members; circuit means for independently exciting eachof said antenna arrays from one of said axially aligned chambers and ashield extending along the longitudinal axis of said chambers for saidcircuit means, each of said chambers having individual tuning means.

8. In a system for feeding a plurality of antenna arrays, a firstsection comprising an outer cylindrical wall; an inner concentric wallformingwith said first wall a hollow chamber, a conductor extendingalong the axis of said walls and a closure terminating said chamber atone end; a second section comprising an outer cylindrical wall, an innerconcentric wall forming with said first wall a hollow cylindricalchamber, said conductor fiaring out at the end of said first hollowchamber and forming said inner concentric wall, and the extension ofsaid first mentioned inner wall forming said second mentioned wall.

9. In a system for feeding a plurality of antenna arrays, a firstsection comprising an outer cylindrical wall; an inner concentric wallforming with said first wall a hollow chamber, a conductor extendingalong the axis of said walls and a closure terminating said chamber atone,

end; a second section comprising an outer cylindrical wall, an innerconcentric wall forming with said first wall a hollow cylindricalchamber, said conductor flaring out at the end of said first hollowchamber and forming said inner concentric wall, and the extension ofsaid first mentioned inner wall forming said second mentioned wall, andan aperture at one end of said first section and means for providingcircuit connections to said conductor through said perforation.

10. In combination, a plurality of antenna arrays, each of said arraysbeing stacked end to end with respect to each other; means includingindependent feeder systems individual to each antenna array forindividually energizing its associated antenna arrays from one end ofsaid stack, and means for precluding electrical interference betweenantenna radiation of said arrays and said feeder system.

11. In combination, a plurality of antenna arrays, each of said arraysbeing stacked end to end with respect to each other; 7 means includingindependent feeder systems individual to each antenna array forenergizingall of said antenna arrays from one end of said stack, eachindividual antenna array comprising a coaxial resonator short circuitedat the upper end thereof, antenna elements coupled into each of theresonators, and a coaxial line for individually driving each antennaarray.

12. In combination, a plurality of antenna arrays, each of said arraysbeing stacked end to end with respect to each other; means includingindependent feeder systems individual to each antenna array forenergizing all of said antenna arrays from one end of said stack, eachindividual antenna array comprising a coaxial resonator short circuitedat the upper end thereof, antenna elements coupled into each of theresonators, and a coaxial line for individually driving each antennaarray from its lower end;

13. In combination, a plurality of antenna arrays, each of said arraysbeing stacked end to end with respect to each other; means includingindependent feeder systems individual to each antenna array forenergizing all of said antenna arrays from one end of said stack, eachindividual antenna array comprising a coaxial resonator short circuitedat the upper end thereof, and antenna elements coupled into itsassociated resonator at half wave intervals.

14. In combination, a plurality of antenna arrays, each of said arraysbeing stacked end to end with respect to each other; means includingindependent feeder systems individual to each antenna array forenergizing all of said antenna arrays from one end of said stack, eachindividual antenna array comprising a coaxial resonator short circuitedat the upper end thereof, and antenna elements coupled into itsassociated resonator, the inner conductor of the resonator for the lowerantenna array being hollow and supporting therein a coaxial line fordriving the coaxial resonator of the upper antenna array.

15. In a system for feeding a plurality of antenna arrays; a pluralityof hollow conducting chambers in axial alignment; circuit means forindependently exciting each of said antenna arrays from one end of saidaxially aligned chambers, and a tuning stub connected to one of saidconducting chambers and forming the energizing connection for the otherof said conducting chambers.

16. In an electrical system, a first and second coaxial hollow conductorforming therebetween a resonant chamber, an extension of said firsthollow conductor, a conductor extending along the axis of saidhollowconductors and forming a hollow conductor coaxial with theextending conductor; said last mentioned conductors forming a secondresonant chamber, a tuning stub for said first mentioned resonantchamber connected to said first and second conductors at aperturestherein, said conductor extending along the axis of said tuning stub andforming the excitation conductor for said second resonant chamber.

17. In an electrical system, a first and second coaxial hollow conductorforming therebetween a resonant chamber, an extension of said firsthollow conductor, a conductor extending along the axis of said hollowconductors and forming a hollow conductor coaxial with the extendingconductor; said last mentioned conductor forming a second resonantchamber, a tuning stub for said first mentioned resonant chamberconnected to said first and second conductors at apertures therein, saidconductor extending along the axis of said tuning stub and forming theexcitation conductor for said second resonant chamber,

and a tuning stub for said second resonant chamber, and form ng theexcitation conductor for said resonant chamber.

18. In a system for an antenna array, a resonant chamber; a feedercircuit including a conductor for exciting said chamber and a shield forsaid conductor extending up into said chamber and terminating at anintermediate section in said chamber, and an enlarged hollow conductorsecured to said conductor at said intermediate section and extendinglongitudinally there rom to form the inner wall thereat of said resonantchamber, whereby said chamber is excited from a point intermediate itsends.

19. In an antenna system. a stack com rising a plurality of antennaarrays, individual feeder circuits, resonant sections for each of saidarrays fed from one side of said system, one of said resonant sectionsterminating one of said antenna structures compriing a hollowcylindrical cond ctor and a second hollow concentric conductor, and atuning stub connected to the co axial resonator associated with thelower antenna structure and containing the central conductor of thelower antenna structure, said tuning stub comprising the central feederfor the upper antenna array.

20. In a system for feeding a plurality of antenna arrays; a first pairof concentric conductors, an antenna array terminating in the chamberformed by said concentric conductors; a second pair of concentricconductors, an extension of the inner conductor of said first pairconstituting the outer conductor of said second pair of concentricconductors and an antenna array terminating in the chamber formed bysaid second pair of concentric conductors, and a central conductorextending along the axis of said first pair of conductors and formingthe inner concentric conductor of said second pair of conductors.

21. In an electrical system, a first pair of conductors comprising aninner and outer coaxial conductor and forming a first resonant chamber,a second pair of coaxial conductors forming a second resonant chamberand comprising an inner and an outer coaxial conductor, an extension ofthe outer conductor of said first pair of coaxial conductors being theinner conductor of the second pair of said coaxial conductors, saidfirst resonant chamber extending from the end of said second resonantchamber, a T-joint in said first pair of conductors, a T-joint in saidsecond pair of conductors, and means for energizing the said first pairof conductors from one branch of said T-joint, and means for energizingsaid second pair of coaxial conductors from said second branch of saidT-joint.

22. A triple-conductor coaxial system comprising an inner and outercoaxial conductor and forming a first resonant chamber, a second pair ofcoaxial conductors forming a second resonant chamber and comprising aninner and an outer coaxial conductor, an extension of the outerconductor of said first pair of coaxial conductors being the innerconductor of the second pair of said coaxial conductors, said firstresonant chamber extending from the end of said second resonant chamber,a T-joint in said triple-conductor coaxial system, a short-circuitingplug in the inner circuit of said coaxial system placed a quarter-wavelength away from said T-J'oint along one branch of said T-connection,input terminals for feeding energy into said outer circuit of saidtriple-coaxial system in the same branch of said T-joint, theshort-circuiting stub placed in the outer circuit of said systemonequarter of a wave length from said T-joint, and input connections inthe same other branch of Tjoint for introducing energy into said innercircuit of said triple-conductor system.

23. In a system for feeding a plurality of antenna arrays, individualfeeder circuit for each of said antenna arrays, a resonant chamherindividual to each of said antenna arrays, each of said antenna arraysbeing connected to their individual resonant chambers for extractingenergy therefrom, and means for connecting each of said individualfeeder circuits to their individual resonant chambers from one end ofsaid antenna arrays without conflicting with the energy fed to the otherof said antenna arrays comprising an outer and. inner coaxial wallforming a first resonant chamber and an inner and outer wall connectedto its individual feeder circuit and forming a second resonant chamber,the outer wall of said first chamber extending beyond the end of saidfirst chamber to form the inner Wall of said second chamber at a sectionbeyond the end of said first chamber and connected to its individualfeeder circuit.

24. In a system for feeding a plurality of antenna arrays, an individualfeeder circuit for each of said antenna arrays, a resonant chamberindividual to each of said antenna arrays, each of said antenna arraysbeing connected to their individual resonant chambers for extractingenergy therefrom, means for connecting each of said individual feedercircuits to their individual resonant chambers from one end of saidantenna arrays without conflicting with the energy fed to the other ofsaid antenna arrays comprising an outer and inner coaxial wall forming afirst resonant chamber and an inner and outer wall connected to itsindividual feeder circuit and forming a second resonant chamber, theouter wall of said first chamber extending beyond the end of said firstchamber to form the inner wall of said second chamber at a sectionbeyond the end of said first chamber and connected to its individualfeeder circuit, and the inner wall of said first chamber extendingbeyond said first chamber and co-axial with the walls of said secondchamber for connecting to the feeder circuit individual to said firstchamber.

WILLIAM E. BRADLEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

